Thermal energy storage device and method for making the same

ABSTRACT

A thermal energy storage device and method for making the same. The thermal energy storage device is in the form of a sealed tube-like container such as a tube-like cylinder or other geometrical configuration partially filled with a phase change material such as calcium chloride hexahydrate. The cylinder is made of tubular high density polyethylene and more particularly an ultra high molecular weight high density polyethylene having a molecular weight of about 500,000 to 700,000 which is tough, chemically resistant, withstands low and high temperatures, acts as a moisture vapor barrier and can be fused and sealed. The calcium hexahydrate is filled in an open top cylinder, closed at the bottom by dissolving two parts of calcium chloride dihydrate with one part of water to provide calcium chloride hexahydrate in liquid form. The cylinder is filled to about 90% by volume and a cap of the same material is then preheated to about fusion temperature. The open top of the cylinder is then brought up to fusion temperature and the cap is fused to it under pressure. The thermal energy storage device with the encapsulated calcium chloride hexahydrate can then be subjected to repeated freeze-thaw cycles. The latent heat of fusion is utilized with sensible heat in various types of usages such as solar heating, heat pump applications and the like. In another embodiment the cylinder may be pinch sealed at the bottom and top by fusion to provide a flat pinch. Modifications of pinch sealing to reduce distortion near the seal include X-shaped, Y-shaped and wave-shaped pinch seal configurations. The tube-like container instead of being cylindrical may for ease in stacking and to present greater surface area take other geometrical configurations such as a generally oblong configuration with rounded sides.

RELATED APPLICATION

This application is a divisional application of my copending applicationSer. No. 76,395 filed Sept. 17, 1979, now U.S. Pat. No. 4,299,274,granted Nov. 10, 1981 which latter application is a continuation-in-partapplication of my co-pending application Ser. No. 35,020, filed May 1,1979 now abandoned.

SUMMARY OF THE INVENTION

In the past various types of phase change materials have been used in avariety of heating installations. These usages have been for thermalenergy storage applications for water heating, solar heating, heat pumpapplications, and the like. The thermal energy storage devices are usedas a means for storing thermal energy under various ambient conditions.The problem in encapsulating the phase change material has undergonevarious investigations and research as the encapsulating material mustwithstand the various stresses provided in the freeze-thaw cycles andpressures and other environmental factors adversely affecting theencapsulating material.

In particular the phase change material calcium chloride hexahydrate hasbeen investigated as it is desireable for use in various domesticinstallations because its melting point of about 81° F. is compatiblewith domestic ambient temperatures. By means of this invention there hasbeen provided an encapsulating material in the form of sealed cylinderof high density polyethylene which withstands high stresses encounteredin the freeze-thaw cycles, the pressures developed therein the variousenvironmental influences against which the thermal energy storage devicemust be designed to withstand attack.

The thermal energy storage device of this invention has been found to beable to withstand the rigors of freeze-thaw stresses. There has beenprovided a stable energy storage device which may be commonly termed athermal energy cylinder or rod. The cylinder is constructed of highdensity polyethylene and more particularly an ultra high molecularweight high density polyethylene having a molecular weight in the orderof 500,000 to 700,000. This material withstands the stresses of thefreeze-thaw repeated cycles and low temperatures and the pressuresdeveloped in the cylinder in the cycles of use.

Further by means of this invention the phase change material such ascalcium chloride hexahydrate has been made useable on a practical basisthrough the novel method for filling the containers such as tube-likecylinders and sealing the same. The calcium chloride hexahydrate isformed from calcium chloride dihydrate in the solid form. In the methodof filling the cylinders, two parts of solid calcium chloride dihydrateare dissolved with one part of water by weight. In the process ofdissolving the heat of solution develops a substantial degree of heat.Thus in changing to calcium chloride hexahydrate a temperature of about130° F. is developed and the calcium chloride hexahydrate is therebymade available in liquid form until it cools below 81° F. The liquid ispoured in an open top bottom end closed cylinder to about 90% of theinterior volume. A cap of the same material as the cylinder is thenpreheated to approximately fusing temperature of about 500° F. whilebeing supported in a hydraulic ram. The top end of the open top cylinderwhich has been partially filled with the calcium chloride hexahydrate inliquid form is then brought up to fusion heat and the cylinder and thecap are fused together under a pressure of about 150 psi.

The closing of the bottom and top ends may also be effected forsimplicity and economy by pinch sealing. The pinch sealing may be eithera flat pinch or to reduce distortion near the fused seal may be in theform of various non-linear configurations comprising X-shaped, Y-shapedand wave-shaped forms of pinching.

The tube-like container instead of being cylindrical may havecross-sections of varying geometrical configurations for ease instacking and to present greater surface area for more efficient heattransfer. One such configuration that is desirable is one of across-section that is generally oblong having rounded sides.

The thermal energy storage device provided by the encapsulating cylinderfor the calcium chloride hexahydrate is after the manufacture by themethod of this invention made available for various types of usages indomestic or industrial installations as desired. The thermal energystorage device is rugged, can be easily handled and may be used in avariety of types of installations wherever a thermal energy storagedevice has a requirement for use.

The above features are objects of this invention and further objectswill appear in the detailed description which follows and will beotherwise apparent to those skilled in the art.

For the purpose of illustration of this invention, there is shown in theaccompanying drawings a preferred embodiment thereof. It is to beunderstood that these drawings are for the purpose of example only, andthat the invention is not limited thereto.

IN THE DRAWINGS

FIG. 1, is a view in elevation showing the method of filling and sealingthe thermal energy storage cylinder.

FIG. 2, is a view partly cut away showing the thermal energy storagecylinder after manufacture.

FIG. 3, is a view similar to FIG. 2, but showing a pinch sealedcylinder.

FIG. 4, is a top plan view of the pinch sealed cylinder of FIG. 3.

FIG. 5, is a top plan view of an X-shaped pinch sealed modification.

FIG. 6, is a top plan view of a Y-shaped pinch sealed modification.

FIG. 7, is a top plan view of a wave-shaped pinch sealed modification.

FIG. 8, is a view in cross-section taken on the line 8--8 of FIG. 3,cross-sectional.

FIG. 9, is a view of a modified tube-like container.

DESCRIPTION OF THE INVENTION

The phase change material used in this invention is calcium chloridehexahydrate. It is formed from calcium chloride dihydrate by mixing twoparts of the dihydrate and one part of water by weight to form calciumchloride hexahydrate. In addition of water to the calcium chloridehexahydrate, because of the heat of solution, a temperature in thesolution of 130° F. is developed. This feature is important, as willappear more fully hereinbelow, in the process of filling and sealing thetube-like container such as a tube-like cylinder of high densitypolyethylene since the melting point is 81° F. for the calcium chloridehexahydrate phase change material and at room temperature it is 72° F.in solid form. Further, in the shipment of the calcium chloridedihydrate to the site of manufacture, the extra weight of the water isin the hexahydrate form obviated and eliminated from the shipment.

The calcium chloride dihydrate used is obtained from The Dow ChemicalCompany as DES, i.e. Dow Energy Storage Compound with nucleating agentto depress the melting point and inhibit supercooling of the liquid formof the converted calcium chloride hexahydrate. The nucleating agenteffectively depresses the melting point from about 86° F. to about 81°F. to a temperature more compatible approximating the room temperaturefor domestic installations and inhibits supercooling to the point wherethe liquid would not freeze and whereby only sensible heat would beprovided. In the thermal energy storage device the latent heat of fusionis desired to be realized in the phase change material to avoid theinefficiency of sensible heat development as much as possible. Thelatent heat of fusion of the calcium chloride hexahydrate is 46 caloriesper gram.

The encapsulating material used in this invention to provide the thermalenergy storage divice is ultra high molecular weight high densitypolyethylene having a molecular weight of about 500,000 to 700,000. Thismaterial is used for the tube-like cylinder provided to encapsulate thecalcium chloride hexahydrate. As an example, the particular ultra highmolecular weight high density polyethylene tubing employed is Driscopipe7600, or 8600 manufactured by Phillips Driscopipe, Inc., a subsidiary ofPhillips Petroleum Company. This material is a thermoplastic materiallending itself to fusing and sealing and has a high degree of stressresistance, toughness, ability to act as a moisture vapor barrier,chemical resistance and ability to withstand high and low temperatures.This high density polyethylene is pressure rated at 73.4 degrees F. tohave high stress resistance and toughness qualities.

As an example, the thermal energy storage cylinder used in thisinvention, is made of Driscopipe 7600 to 8600 in the form of nominal 3inch pipe having an average outside diameter of 3.5 inch and a wallthickness of 0.1 inch. The caps used to seal the bottom and top end ofthe cylinder are made of the same material but have a thicker wallthickness which may vary, but for purpose of illustration may be in theorder of 3/8 inch thickness.

In the method for making the thermal energy storage cylinder of thisinvention, an open top tube-like cylinder 10 as shown in FIG. 1 having aclosed bottom 11 is supported within a jaw-like collar 12 with thebottom resting on the floor. The cap 14 for ultimately closing the topof the cylinder is supported in a ram 16 having set screws 17. The ramis operated hydraulically for vertical movement.

After the open top cylinders have been properly supported, the calciumchloride hexahydrate phase change material is then prepared. In thispreparation the calcium chloride dihydrate with a nucleating agent isused which, per se, forms no part of this invention. Conventionalnucleating agents, such as barium hydroxide may for example be employedas well as the material obtained from The Dow Chemical Company. Thecalcium chloride dihydrate is then mixed with water. In this mixing toform the calcium chloride hexahydrate, two parts of calcium chloridedihydrate are mixed with one part of water by weight in a suitablecontainer. The solution thus obtained develops a temperature of 130° F.when the calcium chloride dihydrate which is in solid form dissolves inthe added water. The calcium chloride hexahydrate in liquid form is thenpoured to a 90% fill in the open top cylinder. The cylinder is thenready for sealing while the calcium chloride hexahydrate is still in theliquid phase.

In the sealing operation a heater 20 is spaced above the open top of thecylinder by an insulating material such as a block of wood 22 to preheatthe cap 14 to approximately 500° F. for the softening of the bottomportion of the cap to prepare it for fusing. The preheating is developedto prevent overheating of the thin cylinder walls at the open top of thecylinder which because of the lesser mass is more easily and morerapidly heated. After the preheating, the block is removed and theheater is used to bring the top portion of the open top cylinder tofusion temperature. When this has been obtained, the heater is removedand the ram is moved downwardly with the cap to apply a total pressureof about 750 pounds which develops a pressure of about 150 P.S.I. on theopen top of the cylinder. This provides a fusion welding of the cap toseal the open top of the cylinder.

The sealed cylinder is then ready for use as a thermal energy storagedevice or cylinder or rod as it may commonly be termed. The 90% fill ofliquid of the interior of volume leaves a 10% void. Upon ultimatefreezing of the phase change material namely, the calcium chloridehexahydrate, a concentration in volume to 80% of the interior volume ofthe cylinder occurs. This then provides a void space of about 20% andprevents too much vacuum being applied which might tend to create unduestresses on the walls of the cylinder. The creation of the void spaceacts as a safety space to alleviate the internal pressures or vacuumthat are developed in the thermal energy storage device upon filling andsealing.

The completed thermal energy storage device is shown in FIG. 2 with theinterior portion shown in the break-away part of the drawing as 80%filled with solid phase change material 24 when subjected to normal roomtemperature at 72° F. The thermal energy storage cylinder with the phasechange material withstands vigorous and repeated freeze-thaw cycles andthe normal wear and tear in shipment and installation and the stressesof a variety of heating installations as desired. The cylinders, asmentioned previously may be of nominal three inch diameter and 6 feet inlength which are not limiting factors but are described for purpose ofexample. Other changes in the wall thickness, diameter and length may bemade as will be apparent to those skilled in the art.

In a modification shown in FIGS. 3, 4 and 8, a cylinder 26 of the samenature as cylinder 10 is first pinch sealed under fusion at the bottomto provide a pinch seal 28. The open top cylinder is then supported andfilled in a similar manner to that described in FIG. 1. The open topwall is then heated in a similar manner and pinch sealed by conventionalvise-like pressure means to provide a fusion sealed pinch closure 30.

Further modifications to provide pinch sealing to reduce distortion ofthe cylinder near the seal are shown in FIGS. 5, 6 and 7. Thesemodifications provide angled or non-linear pinch configurations tominimize any tendencies for thermal distortion. FIG. 5, shows suchmodified cylinder 32 having an X-shaped pinch seal 34. FIG. 6, shows amodification 36 having a Y-shaped pinch seal 38. FIG. 7, shows amodification 40 using a wave-shaped pinch seal 42.

The tube-like container instead of being in cylindrical form may takeother geometrical configurations for ease in stacking and to effectgreater surface area in the walls of the container to effect a morerapid heat transfer. Such a desirable modified tube-like container isdesignated by reference numeral 44 in FIG. 9. This container isgenerally oblong having parallel walls 46 and 48 with rounded sides 50and 52. The cross-section of this container while being generallydescribed as oblong may have rounded corners. When filled the sides orends 50 and 52 may assume the rounded configuration shown in FIG. 9 dueto the internal pressure exerted by the weight of the phase changematerial in the container and the parallel side walls 46 and 48 may havea lesser degree of bulge or slightly rounded shape. The increasedsurface area minimizes cold or hot spot development within the phasechange material through more efficient heat distribution and alsopresents increased space utilization in stacking of the containers.

While this invention has been described with respect to the phase changematerial in the form of calcium chloride hexahydrate, other known phasechange material having melting points and physical characteristicslending themselves to the method of manufacture may be used as will bereadily apparent to those skilled in the art.

Various changes and modifications may be made within this invention aswill be readily apparent to those skilled in the art. Such changes andmodifications are within the scope and teaching of this invention asdefined by the claims appended hereto.

What is claimed is:
 1. A method of filling and sealing a tube-likecontainer with a phase change material to provide a thermal energystorage device which comprises taking the phase change material inliquid form and partially filling a vertically positioned open topthermo-plastic container constructed of high density polyethylene or thelike sealed at a bottom end with said liquid phase change material andfusing by a pinch seal at one end of said container to seal the same,said container being constructed of high density polyethylene having amolecular weight of about 500,000 to 700,000.
 2. The method of claim 1in which the container is filled to about 90% of the open volume withcalcium chloride hexahydrate in liquid form to provide upon freezing ofsaid calcium chloride hexahydrate a filled volume of about 80%occasioned by the contraction upon freezing of said calcium chloridehexahydrate and to provide a void of about 20% of the interior volume ofsaid container to minimize stress upon the walls of said containerduring repeated freeze-thaw cycles and a nucleating agent isincorporated with the calcium chloride hexahydrate to inhibitsupercooling.
 3. The method of claim 1, in which the container iscylindrical.
 4. The method of claim 1, in which the container has anelongated cross-section.
 5. The method of claim 1, in which thecontainer has a cross-section having parallel walls and rounded sides.6. The method of claim 1 in which the pinch seal is flat.
 7. The methodof claim 1 in which the pinch seal is angled.
 8. The method of claim 7in which the pinch seal is X-shaped.
 9. The method of claim 7 in whichthe pinch seal is Y-shaped.
 10. The method of claim 7 in which the pinchseal is wave-shaped.